This invention relates to a vehicle traction control system and, more particularly to such a system which provides for such control by control of both the brakes of the driven wheels and engine torque output.
It is a common experience with automotive vehicles for excessive wheel spin to occur during vehicle acceleration when the operator initiated engine torque delivered to the vehicle driven wheels are such that the frictional forces between the tire and the road surface are overcome. While a small amount of spin between the tire and road surface is necessary in order to achieve a driving force, excessive spin results in the reduction of effective driving force and in the deterioration in the lateral stability of the vehicle.
Various methods have been proposed for preventing an excessive spinning condition of the driven wheels of a vehicle by limiting the slip between the wheel and the road surface at a value that will achieve a maximum transfer of driving force from the driven wheels to the road surface. For example, it is known that excessive acceleration spin can be quickly brought under control by application of the brakes of the spinning wheel. However, in some applications a large amount of energy must be absorbed by the brakes to overcome the excessive torque output of the engine in order to prevent excessive wheel spin. This condition may be required for substantial periods of time.
To relieve the brakes from this high load condition, it has been suggested to also reduce the engine torque output of the engine when an excessive spin condition is sensed. This control is generally slower acting in controlling spin but is effective to minimize the amount and duration of the engine torque that must be absorbed by the wheel brakes in order to limit wheel spin.